TITLE:   GCN CIRCULAR
NUMBER:  37998
SUBJECT: GRB 241030B: COLIBRÍ Upper Limits on the Optical Counterpart
DATE:    24/10/31 07:49:59 GMT
FROM:    Alan Watson at UNAM <alan@astro.unam.mx>

Alan M. Watson (UNAM), S. Antier (OCA), Stéphane Basa (UAR Pytheas),
William H. Lee (UNAM), Dahlia Akl (AUS), Jean-Luc Atteia (IRAP), Nathaniel
R. Butler (ASU), Damien Dornic (CPPM), J.-G. Ducoin (CPPM), Francis Fortin
(IRAP), Simona Lombardo (LAM), Francesco Magnani (CPPM), and Margarita
Pereyra (UNAM)  report:

We imaged the field of GRB 241030B detected by Fermi/GBM, Swift/BAT,
Swift/XRT, and SVOM/ECLAIRs (Fermi GBM Team, GCN Circ. 37980; Klingler et
al., GCN Circ. 37981; Zhao et al., GCN Circ. 37984) during the
commissioning of the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio
Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.

We observed with the engineering test camera in a red filter that
approximates SDSS r. We observed from 2024-10-31 03:51 to 05:46 UTC (9.3 to
11.2 hours after the trigger) and obtained 5160 seconds of exposure. The
data were reduced using custom software and then analyzed and calibrated
against the PS1 catalog using the STDWeb service (Karpov et al., 2022).

We do not detect the optical counterpart (Fu et al., GCN Circ. 37985; Odeh
et al., GCN Circ. 37986; Moskvitin et al., GCN Circ. 37987; Brivio et al.,
GCN Circ. 37991; Moskvitin et al., GCN Circ. 37995) with a 3-sigma limiting
AB magnitude of:

    r > 23.2

We warmly thank the COLIBRÍ engineering team and the staff of the
Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.